Cryogenic air separation systems which employ downflow main condensers typically employ recirculation pumps to ensure adequate wettability of boiling passages during normal as well as part-load operation. Liquid recirculation from the column sump through the boiling passages results in good heat transfer performance as well as enabling satisfaction of the safety criteria of preventing oxygen boiling to dryness. However, recirculation pumps increase cost, reduce reliability and reduce efficiency of the system due to the power penalty incurred to run the pump.